Compositions for use as hydraulic fluids



United States Patent COMPOSITIONS FOR USE AS HYDRAULIC FLUIDS N0 Drawing. Application May 2, 1955 Serial No. 505,519

7 Claims. (Cl. 252-78) This invention is concerned with non-flammable compositions suitable for use as lubricants and for transmitting power .in hydraulic power systems, particularly in aircraft.

There is at the present time a. considerable need for an efiicient hydraulic fluid which is also non-flammable in order that fire and explosion hazards may be reduced to a minimum. This is particularly true offluids for use in the hydraulic system of aircraft and in steel rolling mills and die-casting shops where hydraulic machinery is employed in moving hot equipment or parts. A hydraulic fluid for such uses should also possess low oxidation susceptibility and low corrosion characteristics so that it will not deteriorate in use and will not corrode the materials with which it comes into contact. It is also desirable that the hydraulic fluid should have a low volatility at the elevated temperatures at which it will be used. This temperature may be at least 200 F. For use at low temperatures, for example, of to F., such as are encountered in the operation of aircraft, it is necessary that the hydraulic fluid should possess a low pour point. A low rate of changed viscosity with temperature, i. e. a high viscosity index, is also desirable so that the fluid will operate over a wide range of temperature. The fluid should also possess suificient lubricity and mechanical stability to permit its use in the self 0 lubricated pumps and valves of hydraulic apparatus.

Non-flammable hydraulic fluids have been proposed in 2,862,886 I atented Dec. 2, 195 8 incorporate minor amounts of viscosity index improvers, such as the polymerized esters of acrylic and methacrylic acid, in such phosphate esters.

Hydraulic fluids based on halocarbon compounds and containing a minor proportion of a viscosity index improver such as a polymerized ester of acrylic or methacrylic acid have also been proposed. Such fluids possess excellent non-flammability, low temperature and lubricating properties, but their high specific gravity, which may be as high as 1.9, depending on the halocarbon used, is somewhat of a disadvantage, particularly for aircraft.

The present invention provides a non-flammable composition suitable for use as a hydraulic fluid and having excellent lubricating properties which comprises 15 to 80% by Weight of a normally liquid trialkyl phosphate containing at least twelve carbon atoms in the molecule, 1 to 15% by weight of a polymer of an ester of an acrylic (including alkylacrylic) acid and 10 to by weight of a normally liquid, chlorofluorinated carbon compound containing at least carbon, fluorine and chlorine atoms and, optionally, hydrogen atoms having a boiling. point above C. and a pour point lower than 5 C.

The trialkyl phosphates to be used in the present invention are present in amounts from 15 to by weight and perferably from 30 to 50% by weight. The trialkyl phosphates are preferably those in which each alkyl group has from four to nine carbon atoms. The alkyl groups may be either in a straight-chain or in a branchedchain configuration, the latter being preferred. The trialkyl phosphate employed may contain the same alkyl group in all three positions or it may contain difierent alkyl groups. Mixtures of different trialkyl phosphates may be used. Suitable trialkyl phosphates which may be employed in the compositions of the invention include the tributyl phosphates, trihexyl phosphates, trioctyl phosphates and trinonyl phosphates. A particularly efiective type includes the branched homologues such as tri(2- ethylbutyl) phosphate, tri(2-ethylhexyl) phosphate and tri(3,5,5-tri-methylhexyl) phosphate. The physical characteristics of typical trialkyl phosphates are given in Table I.

TABLE I.-PROPERTIES OF VARIOUS TRIALKYL PHOSPHATES Tri (3, 5, Tri-n- Trl-n- Trl-2- Trl-n- Tri-2 Tri-n- 5-tributyl amyl ethylhexyl ethyloctyl methylbutyl hexyl hexyl) Boiling. point, 0., 1 mm. Hg 113.8 129.1 146. 4 166.1 186. 3 Freezing point, F 1 -50 1 50 1 50 1 50 1 5O Open-cup flash point, F 340 355 410 400 Viscosity, centistokes at 210 F 380 380 445 465 Viscosity, ceutistokes at F 1. 06 1.36 1. 68 1. 76 2. 29 Viscosity, centistokes at 40 F 46. 9 114 240 153 847 Viscosity index 89 91 122 96 1 Lower than.

which the basic constituent consists of one or more esters of phosphoric acid. These esters possess good lubricating properties but are not entirely satisfactory as 0 hydraulic fluids. Thus, the lower trialkyl phosphates exhibit high wear characteristics and are somewhat inflammable, due in part to their volatility. Triaryl phosphates, such as tricresyl phosphate, possess relatively poor viscosity indices and phosphate esters containing both 65 alkyl and aryl groups, such as diphenyl octyl phosphate, exhibit high copper and cadmium corrosion. In order that hydraulic fluids based on phosphate esters should be as non-flammable as possible, it is necessary to employ blends containing a higher proportion of aryl phosphates 70 than alkyl phosphates, but such blends have poor low temperature properties. It has also been proposed to A normally liquid triester of phosphoric'acid containing at least one aryl group may be incorporated in the compositions of the invention in an amount up to 50% by weight to increase the non-flammability. The aryl phosphates may be triaryl phosphates, diaryl monoalkyl phosphates or monoaryl dialkyl phosphates. Preferably the aryl groups are alkyl substituted phenyl groups con taining not more than 5 carbon atoms in each alkyl substituent, such as the tolyl, xylenyl, cumenyl or pseudocumenyl groups. The aryl groups in diand triaryl phosphates may be the same or different aryl groups and the alkyl groups in the dialkyl aryl phosphates may be the same or difierent alkyl groups. Mixtures of the aforesaid aryl phosphates may be used.

a'gseasse employed in the compositions of the invention are tricresyl phosphate and trixylenyl phosphate. Other suitable triaryl phosphates are diphenyl cresyl phosphate, phenyl dicresyl phosphate, diphenyl xylenyl phosphate; diphenylethylphenyl phosphate anddiphenyl o-chlorophnyl phosphate.

Examples of suitable alkylaryl phosphates are octyl diphenyl phosphate, dihexyl cresyl phosphate, octyl phenyl cresyl phosphate and butyl octyl cresyl phosphate. The chlorofluorinated carbon compounds which are used in the compositions of the invention are preferably hydrocarbons in which at least 30% of the hydrogen atoms in the molecule have been replaced by halogen. The non-flammability of the compound improves with increasing halogen content. Compounds with a high halogen content such as the halocarbons also possess fireextinguishing properties which may, on occasion, be of considerable advantage. The halogen compounds may be acyclic or cyclic compounds and may be saturated or unsaturated. v

The stability of the CF bond to chemical reactions, e. g. to hydrolysis and oxidation, makes the chlorofluorinated hydrocarbons particularly suitable compounds for use in the compositions of the invention. The groups CF and CF;, are remarkably stable and appear to enhance the stability of any C--Cl bonds which are situated in close proximity to them. Such stability, particularly to hydrolysis and oxidation, is a very desirable property of hydraulic fluids if formation of acidic compounds and corrosion of metal parts in contact with the fluid are to be avoided. Fluoro compounds containing at least one chlorine atom in the molecule generally possess greater solubility in mineral oils and other solvents and are generally liquid over a wider range of temperature than analogous compounds containing fluorine only.

Suitable acyclic chlorofluoro carbons include those in which at least half the hydrogen atoms of a hydrocarbon have been replaced by fluorine atoms and the rest by chlorine atoms, for example, tetrafluorotetrachloropropane,

or in which at least half the hydrogen atoms are replaced by chlorine atoms and the carbon-chlorine groups are stabilized by CF or CF groups, for example, the perhalopropane of the formula CCl :CCl CF or in which at least half the hydrogen atoms are replaced by halogen atoms in the ratio of at least 3 F atoms to 2 Cl atoms per molecule, as for example, the perhalopentanes of formulae C ClE C ClgF and CsCl F the perlialohexanes of formulae 0 011- c ci ia and C ChF Other suitable species include chloropentafluoroethanes, chlorotrifiuoroethylene, chloropentafluoro-l,3-butadiene, 2,3 dichlorohexafluoro-2-butene, hexachlorotetrafluorobu tanes, trifluorotetrachloropropane, chlorooctafluoropentane, and chlorodecafluorohexane. V I

Liquid products having a boiling point above 75 C. obtained by homopolymerization of unsaturated chlorofluoro hydrocarbons, or by copolymerization of these compounds with other polymerizable unsaturated compounds may also be used. Suitable products are the polymerized difluorovinyl chlorides and the polymerized monochlorotrifluoroethylene sold under the registered trademark Fluorolube.

Preferably, the cyclic compound should have at least one CF group and at least one chlorine atom directly attached to the aromatic nucleus, for example, to the benzene ring. Such compounds are liquid over a wide range of temperatures and show improved compatibility with the other components of the composition as well as increased solubility in hydrocarbon oils. The aromatic nucleus may also carry an ethyl, propyl or butyl group in which hydrogen atoms have been replaced by halogen atoms. Chlorine substituents in these alkyl groups should preferably be stabilized by the presence of a CF, or CF group, as for example in the haloethyl group CClF:CF Examples of suitable cyclic compounds are chloro 1,3-bis (trifluoromethyl) benzene, dichloro (trifluoromethyl) benzene, dichloro bis(trifluoromethyl) benzene and chloro-l-(t'rifluoromethyl)4-(chlorotetrafluoroethyl) benzene. Particularly suitable compounds are trichloro(trifluoromethyl) benzene and tetrachloro- (trifluoromethyl) benzene. These compounds are liquid ove'ra very wide range of temperatures, are highly stable and are non-corrosive to'magnesium, mild steel and copper.

Other suitable species include chloro(difluoromethyl) benzene, trifluoro (cho'r'o'methyl) benzene, (dichlorotrifluoroethyl) benzene, trichloro trifiuorobenzene, dichlorotetrafluorobenzene and pentachloro(trifluoromethyl) benzene.

Some of the physical properties of these-preferred compounds are set out in Table 11.

TABLE II TRICHLORO(TRIFLUOROMETHYL) BENZENE 1 Boiling range, ISO-210 c. (2 Freezing point, ca. 60 C. (3) Specific gravity and viscosity:

Kinematic Tempera- Specific viscosity ture, C. gravity (centlstokes) TETRACHLORO(TRIFLUOROMETHYL) BENZENE (1)' Boiling range, 210250C. (2) Freezing point, 7 C. (3) Kinematic viscosity:

Tempera- Centist'okes ture, C.

va'ted temperatures will leave an oily non'flammable residue of phosphate esters of good lubricating properties.

The incorporation of chlorofluorinated hydrocarbons into" the phosphate esters according to the invention substantially improves the non-flammability properties and can be used either to reduce greatly the low temperature viscosities or, for a given low temperature viscosity, to allow the incorporation of a greater proportion of aryl phosphate ester into the blend at the expense of alkyl phosphate ester, thus remarkedly increasing the nonfla'nimability properties.

The third essential component of compositions of the invention is a polymer of an ester of an acrylic (including alkylacrylic) acid. The aforesaid esters are preferably derived from aliphatic alcohols having from two to fifteen carbon atoms and the polymers may be homopolymers of a single ester or may be copolymers of a mixture of such esters. The term polymer as used herein is intended to be construed accordingly, and is directed especially to polymers having an average molecular weight of a t1ea'st25,000. Typical esters of the polymers which may be so employed are the methyl, ethyl, n-propyl, isopropyl, isobutyl, lauryl, phenyl or benzyl esters of acrylic, methacrylic, l-ethylacrylic and l-propylacrylic acids.

.Polymers of methacrylic acid esters suitable for use in the present compositions are readily available as commercial products and are sold under the trade name Acryloid. They are generally available as concentrated dispersions in a solvent such as alight mineral oil, usually containing about equal amounts of polymer and solvent. These concentrated dispersions can be used as such in the compounding of the present compositions. Typical Acryloid viscosity index improving agents are Acryloid 710, Acryloid HF-855, Acryloid HF-860 and Acryloid HF-8l25. Acryloid 710 is a polymethacrylic ester, wherein the alkylradicals of the ester groups are lauryl and octyl groups as shown in Bos et al. US. Patent 2,681,891.

The above viscosity index improving agents may be present in an amount of from 1 to 15% by weight of the total composition. In general, it is desirable to employ these agents in an amount between 2% and by weight, preferably between 5% and 10% by weight of the total composition.

While the compositions described above exhibit satisfactory corrosion and stability characteristics, it is preferable to include corrosion inhibitors and anti-oxidants to protect the equipment for extended use. It has been found that the combination of an epoxy compound and a sulfurcontaining organic compound is especially effective as a corrosion inhibitor and anti-oxidant for the compositions of the present invention.

The epoxy compounds alone are effective corrosion inhibitors for the compositions of the invention, and may be present in an amount between about 0.5% and 5% by weight of the total composition. Of the epoxy compounds the glycidyl ethers are preferred and of these, glycicyl ethers containing one carbocyclic group directly attached to the ether oxygen atom, such as the glycidyl aryl ethers, provide maximum protection against corrosion, especially of copper and cadmium. Specific glycidyl ethers which may be employed include glycidyl phenyl ether, glycidyl benzyl ether, glycidyl cyclohexyl ether and glycidyl o-cresyl ether. Other epoxycompounds which may be employed include the lower glycidyl alkyl ethers, such as glycidyl methyl ether and glycidyl isopropyl ether, isobutylene oxide, butadiene monoxide, styrene oxide, cyclohexylene oxide, cyclopentene oxide, decene oxide, 2,3- epoxybutane, 1,2-epoxybutane and epichlorhydrin.

While the above epoxy compounds alone are satisfactory, excellent protection against corrosion and oxidation is afforded by their use in combination with a sulfurcontaining organic compound. Suitable sulfur-containing organic compounds for the above combination are the hydrocarbyl sulfides, especially the hydrocarbyl disulfides, such as the dialkyl disulfides and diaryl disulfides, and they may be present in an amount between about 0.05% and 1% by weight of the total compositions. Benzyl disulfide, butyl disulfide and wax disulfide are particularly useful;

The wax disulfide is preferably a reaction product of sodium disulfide and a chlorinated parafiin wax and may be prepared in the following manner. Approximately 5.5 parts by weight sodium disulfide is dissolved in about 2.2 parts by weight of water, the solution is heated and about 0.7 part by weight sulfur dissolved therein with stirring. The resulting solution together with about 5.2 parts by weight of a chlorinated paraffin wax (chlorine content approximately 30% by Weight) and about 10 parts by weight each of denatured alcohol and naphtha are charged into an autoclave and stirred therein at a temperature of about 145-150 C. for 10 hours. The maximum pressure developed is about 220-230 p. s. i. After cooling about 16 parts by weight water are added and thoroughly admixed. Two layers separate upon standing, a naphtha layer and an aqueous layer. The naphtha layer is separated, dried over anhydrous sodium sulfate, filtered and the naphtha distilled off under reduced pressure, the maximum kettle temperature being not greater than C. There are obtained 21.6 parts by weight of wax disulfide as a viscous, oil-soluble, darkcolored liquid. A typical analysis of a wax disulfide employed in the compositions of the invention is set forth below:

Specific gravity 20 C./4 C 1.024 Molecular weight 1050 Sulfur content 1 20-23 Chlorine cont nt 1 1.5-4

1 Percent by weight.

'by weight of an epoxy compound such as glycidyl phenyl ether and between about 0.05 and 1% by weight, preferably between 0.05% and 0.2% by weight, of a hydrocarbyl sulfide such as wax disulfide.

While the above types of corrosion inhibitors are preferred for use in the compositions of the invention, other inhibitors may be used as well. Of these, a salt of a metal of group II of the periodic table and of an aromatic carboxylic acid, an aromatic hydroxy carboxylic acid or a phenol, which salt is soluble in the mixture phosphate ester, halogenated hydrocarbon and polymer to the required extent, is particularly suitable. These salts increase the oxid-ation and thermal stability of the compositions under high temperature conditions of'working. Of the group II metals, zinc and calcium are the most suitable for the present purpose. The aromatic carboxylic acid or phenol chosen should have sufiicient oleophilic properties to ensure that the metal salt employed is soluble in the aforesaid mixture sufficiently to allow a metal content in the finished composition of between 0.01 and 1.0% by weight. Normal or basic salts or mixtures of normal and basic salts may be employed.

The most effective among the metal salts referred to above for the present purposes are the normal or basic zinc or calcium salts of alkylated salicylic acids containing from 12 to 20 carbon atoms, particularly from 14 to 18 carbon atoms, in the alkyl group.

Other inhibitors which may he used are the salts of alkyl malonic acids, condensation products of sulfanols with unsaturated carboxylic, acids, the polyvalent metal salts of hydrocarbon sulfonic acids, amines, aminophenols j and other substituted phenols.

In preparing the compositions of the invention, no special precaution or order of addition of the components is necessary. A suitable method consists in adding an appropriate weight of each component to a suitable vessel, if necessary warming the mixture to about 40 C., and stirring the mixture, when a clear solution is obtained.

The following examples illustrate the compositions of the invention:

Example] A blend was prepared by mixing together 32.5 parts by weight (p. b. w.) of tri(Z-ethylhexyl) phosphate, 32.5

I p. b. W. of tricresyl phosphate, 30 p. b. w. of the trichloro (trifiuoromethyl) benzene of boiling range to 210 C. as described above, and 5 p. b. w. of Acryloid 710.

The blend was a clear, somewhat viscous liquid which had a specific gravity d 1.14, a kinematic viscosity at 130 F. of 9.8 centistokes and at -40 F. of 5,400 centistokesand an autogenousignition temperature: of 4809' C;

Theignition temperature -was.determined by the method ofuASTM D28fi-30gaccordingio which samples: of -the fluid are dropped -into'a heated'flaskunder standard conditions-.until a temperature is -found at which ignition occurs but atr" C. below whichignition failsz to take place.

' Examplell A blend -was prepared fronr 17.5 --p.-b.-w. oftri(2- 3 ethylhexyl} phosphate,- 17.5 p.-b.-w.--of tricresyl phosphate, 60 -p.--b.--w.-ofthetrichloro(trifluoromethyl) benzene used in Example I and 5 p. b. w. -of- Acryloid 710.

A .clear.. .blend .was, obtained which had a specific gravity .4 1.28, .a.kinematic1yiscosity at 130 v F. of 6.1 and ate-40 F. of 730.centistokes and an autogenous ignition temperature .of. 505 C.

Example lII- A-blend was l,prepare,d. from 55' p. b. W. of tri(2- ethylhexyl) ,phosphate, p. b. w. of tricresyl phosphate,.30, 'p. b. w. of thetrichloro(trifiuoromethyl) benzene. used in Example Land 5 p.;b. w. of Acryloid 710.,

The blend was a clear, somewhat viscous liquid which hada specific gravity. d 0 1.08, a kinematic viscosity at; 130 F. of 8.4 and at -40 F. of, 1,500 centistokes and anautogenous ignition temperature 0f 422 C.

Example IV A blend was prepared from 30 p. b. w. of tri(2- ethylhexyl). phosphate,-5 p. b. w. of tricresyl phosphate, 60 p. b. w. of'the trichloro(trifiuoromethyl) benzene used in Example I and 5 p. b.,w. of Acryloid 710.

The blend was a clear, somewhat viscous liquid which had a specific gravity (1 1.22 and a kinematic viscosity at 130 F.- of 5.7 andat 40 F. of-478 centistokes and an autogenous ignition temperature of 428 C.

Example V This blend was prepared from 45.5 p. b. w. of tri(2-. ethylhexyl) phosphate, 19.5 p. b. w. of tricresyl phosphate, p. b. w. of the trichloro(trifluoromethyl) benzene used in Example I and 5 p. b. w. of Acryloid 710.

The-blend was a clean-somewhat viscous liquid, which had aspecific gravity r1 3 1.10, a kinematic viscosity at 130 F. of 8.4 and, at F. of 2,380 centistokes andan autogenous ignition temperature of 440 C.

Example. .VI

This blend was prepared from 32.5 p. b. w. each of tri (2'-ethy1hexyl) phosphate andtricresyl phosphate, 30

p. b. w.. of the. tetrachloro(trifiuoromethyl) benzene, boiling range 210" to 250 C. as described above, and 5 p. b. w. of Acryloid 710.

The-blend was a clear, somewhat viscous liquid which had a specificigravity d 1.16, a kinematicviscosity at ,130.F.jof 11.7 and at -40, "F. of 19,000centistokes, and an autogenous ignition temperature of 455 C.

Example .VII

Example VIII A blend was prepared from'30 p. b. W. of tri(2- ethylhexyl) phosphate,.5 p. b. W. of tricresyl phosphate, pub. w. of the tetrachloro(trifiuoromethyl) benzene usedinExampleVLQandv 5 p. b. w. of Acryloid 710.

The blend was a clear, somewhat viscous liquid which iii at F. of 8.1 and at .,40.=" F. of.2,600 'centistokes,:.

and an autogenous ignition te'mperaturewfi5425-" Cir While the compositionslof -Examples kl ItoP VIIIi are satisfactory as regards stability; iexcellentprotection-z against oxidation during prolonged ..use :andtthc com... sion of metal parts in contact withthex fluids isafiorded. by incorporating about 0.9% i by weight .ofzrglycidyl. phenyl ether and about 0.1%=by -weight of a -wax.:disulfide prepared asdescribed above, or a .normaltor. basic salt of a metal of group II of the periodietableuand' of an. aromatic carboxylic 'acid, aromatic hydroxycar-fl boxylic acid or a phenolasdescribed above injarnount sufiicient to give a metal content of between. 0.01. 'andi 1.0% by weight of the finishedcompositionn We claim as our invention: 1. A substantially non-flammable"composition-of mat ter for use as a hydraulic fluid comprising Percent by weigh Tri(2-ethylhexyl) phosphate p- 32.5 Tricresyl phosphate 32.5

A viscosity index-improving polymerized ester-of C aliphatic monohydricv alcohol and meth-, acrylicacid having an average. molecular weight greater. than. about 25,000

Trichloro(trifiuoromethyl) benzene 30 2. A substantially non-flammable composition of matter for use as a hydraulic fluid comprising Percent by weight Trioctyl phosphate 30-50 Tricresyl phosphate 5-35' A viscosity index-improving,polymerized ester of C 4 aliphatic monohydric alcohol and methacrylic acid having an average molecular weight greater than about 25,000 5-10 Trichloro(trifiuoromethyl) benzene 30-60 3. A substantially. non-flammable composition-of mat ter. for. use asa hydraulic fluid comprising.

Percent by weight A trialkyl phosphate wherein each alkyl radical has from 4 to 9 carbonatoms 30-50 A triarylphosphate containing from 18 to 33 carbon atoms per. molecule 5-35 A viscosity index-improving polymerized ester of C to C aliphatic alcohols .andmethacrylic acid having an average molecularweight of at. least about 25,000

A chloro(fluoromethyl) benzene having a boiling:

point above about 75 C. and a pourpoint below about..5 C 30-60 4. Asubstantially non-flammable composition of matter for use as a hydraulic'fluid comprising s-io- Percent by weight. Trioctyl phosphate 3050.. Tricresyl phosphate 5-35 A viscosity index-improving polymerized ester of C aliphatic monohydric alcohol. and methacrylicacid having'an average-molecular weight greaterthan about 25,000 510 Chloro(trifluoromethyl) benzene 30-60.

5. A substantially non-flammable composition of matter for use as a hydraulic fluid comprising Percent by weight T rioctyl phosphate 30-50 Tricresyl phosphate 535 Aviscosity index-improving polymerized ester of C aliphatic monohydric alcohol and methacrylic acid having an average molecular weight greater than about 25,000 5-10 Tetrachloro(trifluoromethyl) benzene 30-60 9 10 6. A homogeneous composition of matter for use as a Percent by weight hydraulic fluid comprising A trihydrocarbyl phosphate containing between Percent by weight about 12 and about 36 carbon atoms per mole- A trialkyl phosphate wherein each alkyl radical cule, at least 0116 Of the hydfocafbyl radicals contains 4 to 9 carbon atoms 15-80 5 ing n ryl r i 3 A trihydrocarbyl phosphate, at least one of the Viscosity index-improving polymerized esters of hydrocarbyl radicals of which is an aryl radical -50 4 to 18 alcohols and mFthacl'ylic acid having Viscosity index-improving polymerized esters of an average molecular welght of at least about C to C alcohols and methacrylic acid having an average molecular weight of at least about A chltmlmfluommethyl) benzine havmg bolling point above about 75 C. and a pour 25000 1 15 point below about -5 C 30-60 A chloro(fluoromethyl) benzene having a boiling P above z 75 o and a Pour 1mmt 0 References Cited in the file of this patent belw 5 C 1 UNITED STATES PATENTS 7. A substantially non-flammable composition of mat- 2, 524,590 Boe Oct. 3, 1950 ter for use as a hydraulic fluid comprising 2,549,270 Watson Apr. 17, 1951 2,583,588 Mosteller Jan, 29, 1952 Percent by weight 2,707,176 Gamrath et a1. Apr. 26, 1955 A trialkyl phosphate wherein each alkyl radical 2,710,842 Husig et a1. June 14, 1955 contains 4 to 9 carbon atoms each -50 2,719,129 Richardson Sept. 27, 1955 

3. A SUBSTANTIALLY NON-FLAMMABLE COMPOSITION OF MATTER FOR USE AS A HYDRAULIC FLUID COMPRISING 